The invention relates generally to a monitoring system.
More particularly, the invention relates to an optical monitoring system having a day-night black and white and color video camera.
For the surveillance of objects, e.g., structures and apparatus located inside structures or distributed over large areas, it is known to use video cameras which continuously produce images on monitors. In addition to black-and-white video cameras, it is attempted to employ color cameras for monitoring systems because of the greater amount of information available therefrom. It is known, however, that black-and-white cameras require much lower light intensities than color cameras. In other words, color video cameras are considerably less sensitive to light than black-and-white cameras.
Accordingly, difficulties arise when monitoring with a color video camera during the night hours. At night, a color video camera must be furnished with light of much greater intensity than that required for a black-and-white camera. Due to the greater illumination intensities, energy costs are significantly increased. To save energy, it is known to use separate light sources and cameras for large objects being monitored. Here, only the light sources for the particular camera in operation are switched on. Thus, continuous illumination of all portions of an object being monitored is avoided and only limited areas are illuminated at any time.
It is also known to activate light sources only when needed in response to alarm signals. However, it is desirable to produce images of objects being monitored without interruption.